The present invention relates generally to oil seals, molds and methods for making such seals, and more particularly, to molds and methods for making oil seals which are especially adapted to provide improved so-called secondary sealing performance in combination with positive centering, ease of installation and reduced cost without compromise of performance in use. These objectives are achieved by providing a mold and method for making seals of the above type.
With the passage of time, and with the advent of increasingly complex drive units, particularly automotive engines and drive trains, the need for improved seals has continued. Many, if not all, modern automotive and related engines are now being called upon to perform in environments which are much more destructive of seals and other rubber accessories than has heretofore been the case.
Requirements of decreased pollution potential, for example, cause automotive engines to be operated at much higher temperatures than was previously the case. In addition, automotive oil seals are frequently called upon to resist lubricants having additives and other ingredients which are detrimental to the life and/or performance of many elastomers.
Consequently, improved machine designs have made concomitant demands for improvement in oil and other fluid seals. As a consequence of this demand, many oil seals have been proposed or tested which incorporate improved materials, principally so-called fluoroelastomers. These materials are attempts to combine the desirable physical and engineering properties of known elastomers such as resiliency, resistance to compression set, elongation and proper hardness, with properties usually more characteristic of non-elastomers, such as resistance to chemicals, high temperatures, and oxidation or other deterioration.
Many such compounds were not available until recently, and it was and is considered difficult to formulate an elastomer which has excellent chemical and high temperature resistance combined with low temperature flexibility, for example. More recently, certain high performance fluoroelastomers have been developed, but these elastomers, while very satisfactory from many aspects of performance, are extremely expensive in use. Accordingly, while the cost of the elastomer component per se has not previously been a very significant part of the cost of most oil seals, elastomer prices ranging from $5 to $10, and in some cases, up to $100 per pound, have created the need for closer control costs to achieve significant economy in the use of such expensive materials. The present invention provides seals which use minimal amounts of expensive materials.
Referring now to another aspect of modern oil seals, there has been in the past a trend toward and away from so-called rubber outside diameter seals, that is, seals wherein the secondary seal between the seal-receiving counterbore and the seal itself is achieved by contact between rubber on the outside of the seal casing and the metal of the machine counterbore. The requirements for performance in use have caused users to alternate between specifying rubber and metal outside diameters. The advantage of rubber is sometimes that of increased reliability of insertion and occasionally better secondary sealing. However, there are other advantages to metal outside diameters which possess actual or potential advantages. These include the ability to locate the inside diameter of the seal per se more accurately, because this part is often formed with respect to a metal casing outside diameter. Forming a rubber outside diameter ("OD") can cause difficulties in insuring that the diameters of both the rubber outermost diameter and those of the casing are properly centered with respect to that of the seal lip body.
A disadvantage of a rubber OD seal is that, when making an installation, the cylindrical rubber element which forms the outside diameter is placed in shear. Hence, after the seal is installed to a nominal depth in its associated counterbore, the forces urging it into position are released and the seal tends to "pop back" to a position lying axially outwardly of the specified position. This can sometimes cause axial misalignment and improper or indefinite positioning of the seal.
Consequently, there are certain applications wherein it is highly desirable to provide a seal having the best features of both a metal outside diameter, namely, positive seating, and particularly a flash-free metal OD, and those having the advantages of a rubber outside diameter, which include improved secondary sealing and ease of installation.
With seals wherein it has been attempted to make a combination rubber and metal OD, that is, where there is a heel gasket of rubber having the same OD as the metal portion, prior molding methods have been such that rubber flash or scrap has been formed on the metal OD. This may compromise the ability of the metal OD to engage the metal of the counterbore in a proper way. Hence, it has been common to posttreat these seals by scraping or wire brushing the flash or scrap from the metal OD. This is a disadvantage insofar as it requires an extra operation and insofar as the metal OD may be damaged by removal of a surface coating therefrom or otherwise during this operation.
According to the present invention, a design is provided which combines the advantages of having rubber and metal on the seal outside diameter, together with the most economical use of materials including the expensive rubber materials required to form such seal OD. Further, molds and molding methods are provided to manufacture such seals reliably at low cost.
In view of the failure of the prior art to provide a seal combining certain of the above features is an economical design, it is an object of the present invention to provide an improved oil seal.
Another object of the invention is provide an improved mold which is suitable for making oil seals according to the invention.
Still further, it is an object of the invention to provide an oil seal which includes a rigid casing having one part of its outside diameter adapted to engage and position the seal with respect to an associated counterbore, and another, reduced or minor diameter portion which serves as a bonding surface for a cylindrical rubber outside diameter secondary sealing element.
Another object of the invention is to provide a seal having a casing having two outer diameter portions, which includes a fluoroelastomer coating on the exterior of the smaller of the two diameters and wherein the larger diameter is substantially free from elastomer.
Yet another object of the invention is to provide a seal wherein the rubber outside diameter is formed by flowing rubber, during molding, from the elastomeric seal lip area to the outside diameter only along one surface of the casing, using the casing as an element of the mold cavity, and making it possible to make both the seal lip body and the outside diameter heel gasket from the same charge of material.
A further object of the invention is to provide an oil seal having fluoroelastomer principal sealing lip body as well as a fluoroelastomer heel gasket and which uses minimal amounts of material to provide these elements, in the interest of achieving maximum economy.
A still further object of the invention is to provide a mold for seal making, which mold includes first and second, relatively movable elements, one of which includes a plurality of casing support units, which serve to position the casing within the molding cavity and also assist in defining plural passage between the portion of the mold cavity defining the seal lip body and the portion defining the heel gasket so that the two elastomeric elements of the seal may be made in a single operation from a single charge of elastomer.
Another object of the invention is to provide a seal mold wherein opposed cooperating surfaces on two relatively movable mold elements are constructed and arranged so that, when a seal casing of suitable dimensions and wall thickness is positioned in the mold, the flash barriers will be established to aid in defining fluid-tight cavities for the formation of the heel gasket and portion of the sealing lip respectively.
Yet another object of the invention is to provide a mold having relatively fixed and movable parts, one of which includes a coining ring or like annular surface on one portion thereof and a flash barrier forming surface on another part thereof, such movable part being adapted to engage a sealing casing and seat it in a desired position within the mold while at the same time positioning it relative to a counterpart surface on the other, fixed portion of the mold, whereby flash barriers are established on opposed surfaces of the same casing element.
Another object is to provide a mold as described above wherein the flash barrier surfaces are formed on opposite sides of a major diameter portion of a stepped seal casing.
A still further object of the invention is to provide a mold having opposed flash barriers and means for positioning a casing within a part of the cavity, which mold parts are adapted to cooperate with a third, independent relatively movable member which is adapted upon mold closing to transfer fluent curable elastomer from a region outside the molding cavities to the molding lip and heel gasket forming areas of the cavity interior.
A further object of the invention is to provide a mold and method wherein the seal casing may have a radial flange of a given thickness and a mounting flange of a reduced wall thickness, and wherein the mounting flange wall is drawn or ironed to achieve more accurate control of such wall thickness for the purpose of eliminating flash and for facilitating mold closure and removal of the finished part.
A still further object of the invention is to provide a method of making an oil seal which includes forming a casing having walls which include major and minor outside diameter flanges, positioning such casing in a mold dimensioned so that the outer surface of the major diameter casing wall is engaged by a flash barrier on a fixed part of the mold and, prior to filling the mold cavity, engaging in an inner surface of the major diameter casing wall with a flash barrier forming surface on a movable mold member, moving the movable mold member so as to engage and seat the casing with respect to the casing support elements on the fixed mold part, thus subdividing the molding cavity into a seal body forming portion and a heel gasket forming portion, with such cavity portions being connected to each other by way of spaced apart passages defined in part by the casing support elements, and filling both the mold cavity portions with fluent curable elastomer and curing said elastomer to form a seal body and a heel gasket bonded to said casing.
The invention is carried into practice by providing a mold having at least two relatively movable parts and having surfaces which, in combination with a seal casing, define the shape of one mold cavity having a portion in the form of a seal lip body and another portion having the shape of a heel gasket, with the two cavities being in communication with each other through plural passages, and with the movable mold parts including spaced apart flash barrier surfaces adapted to engage opposed surfaces on the interior and exterior walls, respectively, of the seal casing's major diameter.
The manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings wherein like reference numbers indicate corresponding parts throughout.